Existing solid state fixtures including light emitting diodes (“LEDs”) commonly include power supplies that utilize offline power converter topologies and operate in an open loop manner. The power supply may include a microcontroller (μC) that stores a power curve and outputs a pulse-width modulated (PWM) signal as a control signal to a power factor control (PFC) chip, which adjusts wattage of the buck power converter over a universal input voltage range from 90 volts AC to 480 volts AC. PFC chips may typically have tolerances of up to about 12% with respect to gain. Moreover, the forward voltage drops of LEDs also vary by bin and drive current. As a result, it is usually necessary to rework and/or change resistors within the power supplies of existing solid state fixtures during manufacture to adjust the power rating of the supply/fixture to meet desired specifications prior to finalizing the product for shipment or consumer use so that the supply/fixtures are calibrated to emit light having brightness that meets desired specifications. Such rework may be a time consuming and inefficient process, and may result in problems when the AC input voltage is above or below its nominal value or on the low end of an electronic low voltage (ELV) dimmer, where inconsistencies in drive current may visibly appear from fixture to fixture. Typically solutions to these problems include limiting low end dimming to obscure low end inconsistencies in driving current. This would however result in dead travel near the low end of the dimmer.
Thus, it would be desirable to provide a solid state lighting system that maintains consistent lighting current and brightness over time, reduces or eliminates the need to rework supply/fixtures during manufacture, enables consistent low end dimming of cascaded fixtures, improves dimmer compatibility and/or and sets a hard upper limit for lighting current.